Effect of an air layer on the insulation performance at the interface between epoxy resin and silicone rubber

We have proposed a concept of an environment-conscious all-solid-insulated substation system as a next generation substation. In order to make the system compact and its layout flexible, it is required to develop a compact connection system with solid insulating materials. A hard and a soft insulating material are to be used for this connection system. Therefore, there is a concern about air penetration into their interface at the time of connection, which reduces the insulation performance. In order to simulate this situation, a model connection part was made using an epoxy resin board as the hard material and a silicone rubber board as the soft material with a spacer inserted into their interface. The present paper reports experimental results on the breakdown strength under ac and impulse voltages. It is confirmed that the insulation performance decreases with an increase in the thickness of the air layer between the two boards.